Yes, I have experience with multiple layers of back-to-back MC-LAG as you are 
describing with a similar product set, EX9200 (basically an MX) as core and 
QFX5k as aggregation and access.

It worked “ok” for the most part however, we were pushing numbers on this setup 
beyond what 99% of customers ever would which meant we got to experience the 
weird and wonderful failures, mostly related to memory leaking or buffer 
exhaustion (and when it went bang it REALLY went bang).

In 2018 I couldn’t in good faith advocate this back-to-back MC-LAG over 
multiple tiers setup to anyone. If you need L2 adjacency between your access 
switches then stitch it up using EVPN on your QFX’s. 


Sent from my iPhone

> On 13 Mar 2018, at 12:21 pm, Karl Gerhard <> wrote:
> Hello
> I would like to know whether anyone has deployed a two-tier MC-LAG:
> MC-LAG #1 between the aggregation switches
> MC-LAG #2 between the core routers
> This would allow for a network design with "active/active everything".
> Our current setup is the following: Access (Juniper EX), Aggregation (Juniper 
> QFX), Core (Juniper MX).
> Our access switches use Redundant Trunk Groups to connect to two aggregation 
> switches.
> Each aggregation switch has an AE where the first cable of the AE goes the MX 
> #1 and the second cable of the AE goes to MX #2. To make this possible we 
> have an MC-LAG between the MXs.
> Pic:
> With this setup only one uplink of the access switch is utilized, the other 
> one is idle due to the nature of redundant trunk groups (active/passive).
> If we had a second MC-LAG between the QFXs we could utilize both uplinks of 
> the access switch.
> Pic:
> Does anyone have experience with such a setup? Is this the highway to 
> debugging hell or is it a good idea that increases bandwidth available to the 
> access layer?
> Regards
> Karl
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